Neutrophil Extracellular Traps Contribute to Peri‐Implant Bone Loss: Insights Into Pro‐Inflammatory Macrophage–Neutrophil Crosstalk

AIMS: To investigate the contribution of neutrophil extracellular traps (NETs) to peri-implant bone loss and explore upstream cellular mechanisms associated with aberrant NETosis. MATERIALS AND METHODS: Clinical specimens were analysed for NET formation and inflammatory markers. A rat peri-implantitis (PI) model with local DNase I treatment was used to evaluate the contribution of NETs to peri-implant bone loss. Single-cell and spatial transcriptomics, cell-cell communication analyses and functional experiments were integrated to investigate macrophage-neutrophil interactions. RESULTS: NET-associated markers were increased in PI specimens and correlated with inflammatory cytokines. DNase I attenuated peri-implant bone resorption and inflammation in rats. Integrated transcriptomic analyses identified a NETosis-associated neutrophil subpopulation (NNeu) with a prominent NET-forming phenotype. Spatial proximity and cell-cell communication analyses identified pro-inflammatory macrophages (PMac) as a candidate upstream population. Mechanistically, PMac-derived macrophage migration inhibitory factor (MIF) promoted NETosis through CD74-p38 MAPK signalling in vitro, while experimental modulation of MIF-CD74 signalling in vivo was accompanied by corresponding changes in NET formation, inflammation and peri-implant bone loss. CONCLUSIONS: NETs contribute to inflammatory bone loss in an experimental PI model. in vitro findings further suggest that pro-inflammatory macrophage-neutrophil crosstalk regulates NET formation through MIF-CD74-p38 MAPK signalling, highlighting a potential immunomodulatory target.